What kind of dog should I get?

I am getting a dog, but I don't know what kind I should get. I have 2 nieces that I always see and they're probably going to see my dog all the time. So I need a dog that is good with children under the age of 10. I also have many cousins that are still babies so I would like the dog to be good with them too. I would also like a dog that doesn't mind snuggling with kids and also I would like to leave the dog alone with the children. I need a dog that is easily trainable and very intelligent. I would also like a small dog that is 20 pounds or less. THANK YOU!!